1. Field of the Invention
The present invention relates to an amplifier circuit in a CMOS integrated circuit and, more particularly, to a differential amplifier circuit.
2. Description of the Related Art
Presently, in a CMOS integrated circuit, alternating signals are normally amplified using a CMOS inverter. For example, in a quartz oscillation circuit as shown in FIG. 1, an oscillation output of a CMOS inverter X1 at a first stage accompanied by a quartz oscillator X't connected across input and output terminals thereof is sent to subsequent stages after being amplified further by a CMOS inverter x2 as a buffer circuit.
The potential of an operating point of the oscillation output of such a CMOS inverter fluctuates owing to process-related factors, fluctuation of power supply potential caused by the oscillation operation and the like to be out of a predetermined threshold of the CMOS inverter X2. It has been therefore difficult to set the duty ratio of the oscillation output at 1/2, and the duty ratio has been set in a certain allowable range.
A limitation is sometimes placed on the value of a current supplied to the CMOS inverter X1 in order to reduce power consumption. In such a case wherein the voltage amplitude of the oscillation output is reduced, the influence of the fluctuation of the operating point potential on the duty ratio becomes too significant to ignore.